My iPhone presence sensor works fine. My wife’s SmartThings Location Services setting keeps changing from ‘Always’ to ‘While Using the App.’
Running the latest version of the ST classic app on an iPhone 6s running the latest version of iOS.
I’ve tried:
-Log out and back into ST
-Delete and reinstall ST
-Remove and add the iPhone presence sensor device
-Hard boot the phone
are you saying if you change the setting to Always, close the screen, go back to that screen that the setting has changed to While using the app? or does it change over a longer time frame?
you know we are going to ask you to post what versions you have for both 
under settings > privacy > location services > system services → check that nothing obvious has been disabled?
any other apps showing as Always on her iPhone… just checking if it is only limited to the ST app.
The setting does not immediately revert from ‘Always’ to ‘While Using the App.’ It reverts at some point over the course of 24 to 48 hours.
Location Services -> System Services settings are identical to my iPhone.
Other apps are set to ‘Always.’ ST is the only app exhibiting this behavior.
The same thing was happening with my wife’s iPhone 6s. I finally gave up and migrated to the new Smartthings app, but with this one even though the setting stays at “Always” the presence detection isn’t working. This is very very annoying, since most of my automations key off whether or not anyone is at home.